Long process to treat water

Turning sewage into something clean enough to release into a river requires multiple stages of treatment.

And before groundwater, reservoir water or river water can be used as drinking water, it must go through a separate multi-step treatment process. The intensity of the treatment depends largely on the source of the water, experts say.

Here's how North Jersey's sewage treatment and drinking water treatment plants typically work.

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The Bergen County Utilities Authority sewage treatment plant in Little Ferry, on the banks of the Hackensack River, handles 65 million gallons of raw sewage every day from 500,000 residents in 47 Bergen County towns.

The arriving sewage first passes through screens made of vertical steel bars to capture large debris such as rags, glass and rocks. Next, it gets pumped into chambers where the sewage slows down, so that small inorganic material, such as sand and grit, can sink to the bottom.

The sewage is slowed further in a series of 16 large, rectangular primary treatment tanks, about 100 feet long and nearly 8 feet deep, so that heavy organic material – yes, poop -- sinks to the bottom, while lighter solids such as oil, grease and soap scum float to the top. This step removes about 40 percent of the pollutants, said Stephen Askew, director of water pollution control for the authority.

The floating scum gets skimmed off the top of the water with mechanically controlled horizontal metal bars and sent to a landfill. Some is retained and put into anaerobic digestors where microorganisms break it down and produce methane, a natural gas. The methane is captured and burned in several units that generate enough electricity to cover about 40 percent of the treatment plant's energy needs.

Meanwhile, the heavy solids at the bottom of the 16 primary tanks are removed, dewatered, and shipped to another treatment plant in Newark that handles sludge. A million gallons of sewage generates about 250 pounds of solids, Askew said.

Next, the partially cleaned effluent moves to a series of concrete raceways or aeration tanks, which are injected with bacteria and other naturally occurring microrganisms, along with oxygen, a method called the activated sludge process. The oxygen helps the organisms in the sewage to thrive, reproduce and consume organic matter in the sewage stew. The injected oxygen roils up the sewage, making the raceways look like rivers of bubbling chocolate in a Willie Wonka factory.

The sewage and bacteria mixture flows from the aeration basins to sedimentation tanks, where colonies of the microbes settle out to the bottom. The microbes get recycled back to the aeration tanks to perpetuate the process.

By the end of this second stage, which removes 50 percent of contaminants, the effluent looks as clear as drinking water, though it is not quite as clean. At this point, chlorine is added to the effluent to disinfect it, killing any pathogenic bacteria or viruses. The facility uses about 5,000 gallons of chlorine a day.

But since chlorine can harm fish and other aquatic life in the river, an additional chemical, sodium bisulfate, is added to neutralize much of the chlorine.

The entire process takes six hours.

The treated effluent then gets released into the Hackensack River.

"We treat it so it has no impact on the river," Askew said. "If the river water is pristine, my job is to keep it pristine. Sometimes the effluent is even cleaner than the river water."

To ensure that industrial customers don't dump something down the drain that the treatment plant can't handle, the authority issues them permits and routinely monitors the industrial sites’ discharges. In some cases, the sites need to pre-treat sewage before releasing it into the public system.

The treatment process at the Two Bridges Sewerage Authority facility in Lincoln Park is similar, though there are more steps, since Two Bridges releases its effluent into the Pompton River, a fresh water body that has less volume than the Hackensack. In addition, the pump station to send river water back to the Wanaque Reservoir is just a stone's throw downstream from Two Bridges’ effluent outfall pipe.

Sewage at Two Bridges goes through the activated sludge process twice. After being screened to remove grit, the wastewater is mixed with sludge that had been removed from previous wastewater to create a combination called "mixed liquor" by the industry. Oxygen is also added. Introducing the sludge also introduces bacteria that can reproduce rapidly since it has plenty of food as well as the introduced oxygen. After several hours, the bacteria have consumed much of the organic matter in the sewage, and the organisms settle to the bottom of the tank, separating from the clearer water.

The Two Bridges facility goes through this process twice for each batch of raw sewage it treats.

In addition, polyaluminum chloride is added to remove phosphorous, a nutrient that can cause algae blooms and reduce oxygen levels when released with the effluent into the river water.

After the organisms settle out, the treated wastewater is pumped through large room-sized filters, composed of sand, gravel and anthracite coal, which help capture any remaining solids. The treated wastewater is clean enough to meet permit standards before going through the filters, but they are an extra step to get the wastewater even cleaner, said Ernest DeGraw, the plant superintendent.

Finally, instead of using chlorine for disinfection, the Two Bridges facility shines ultraviolet light on the treated wastewater. That eliminates the possibility for any chlorine to enter the river with the effluent, and eliminates the need to use an additional chemical to neutralize the chlorine.

The facility is investing $17.5 million on utility and backup power upgrades along with a new pump station and headworks facility – the area where the sewage first reaches the plant. The plan includes a new grit removal facility with bar screens to better remove inorganic material, such as disposable baby wipes. Though wipes are often advertised as flushable, they don't break down the way toilet tissue does and can clog pump mechanisms, which adds cost to the treatment process and can put staff at risk.

Although drinking water treatment plants follow some very similar steps, some must do more than others to meet drinking water quality standards based on the source of their water. "Every plant is designed around its water source," said Joseph Bella, director of the Passaic Valley Water Commission.

As water travels down the Hackensack River and reaches the Oradell Reservoir, pumps suck up to 80 million gallons a day during the winter and double that during summer into the treatment plant on the banks of the reservoir operated by Suez, the for-profit water company that serves most of Bergen County.

The first part of treatment at the plant is rather simple: The water passes through large screens that catch anything that could get clogged in the pumping machinery – twigs, leaves, even fish.

Then sulfuric acid is introduced to lower the water's pH, said Rick Tecchio, superintendent of system support for Suez's New Jersey operations. If the pH is too high, the water is more alkaline, which can affect taste and corrode plumbing.

Next, a coagulant is added to the water so small solids bind together, making them easier to remove, Tecchio said.

Ozone is added to remove iron and manganese. Then the water flows into basins and air is pumped in. This process, called dissolved air flotation, forces remaining solids to the surface, so they can be skimmed off. After the dissolved air floatation process, sodium hypochlorite is added for disinfection.

The water gets pumped into large rectangular tanks that serve as filters, each filled with three layers of material – bits of anthracite coal, coarse sand, and fine sand. Any remaining solids bind to the granules as the water percolates down through the materials.

Finally, a small amount of sodium hypochlorite and sodium hydroxide are added to the water as it leaves the plant.

The entire process takes about five hours.

Some treatment sites will use chlorine or ultraviolet light to help disinfect water.

Most standard sewage and drinking water treatment facilities are not equipped to remove contaminants of emerging concern, such as steroids and pharmaceuticals flushed down the drain, as well as the microbeads in personal care products.

Drinking water treatment facilities that use sewage effluent must add more steps to make the water clean enough to drink. The Orange County Water District's facility in California, for instance, includes a process called reverse osmosis. The water gets squeezed at high pressure through membranes made from semipermeable plastic, which removes dissolved chemicals, lead, pesticides, viruses and pharmaceuticals in the water.